Cabin pressure control



y 3, 1961 a. E.'DEL .MAR Re. 24,990

CABIN PRESSURE CONTROL Original Filed May 16, 1942 s Sheets-Sheet 1muhnum I t 67 I. a r

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ATTORNEY.

B. E. DEL MAR CABIN PRESSURE CONTROL May 23, 1961 3 Sheets-Sheet 2Original Filed May 16, 1942 A NEED/D INVENTOR. ERA/CE E. 054 M42 May 23,1961 a. E. DEL MAR CABIN PRESSURE con-mm.

3 Sheets-Sheet 3 Original Filed llay 16, 1942 INVENTOR. 520:: t. 054 M42BY p7 United States Patent CABIN PRESSURE CONTROL Bruce E. Del Mar, LosAngeles, Calif., assignor to Doug- Ias Aircraft Company, Inc., SantaMonica, Calif.

Original No. 2,549,672 dated Apr. 17, 1951, Ser. No. 443,233, May 16,1942. Application for reissue Sept. 15, 1953, Ser. No. 380,385

38 Claims. (Cl. 981.5)

Matter enclosed in heavy brackets appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

My invention relates to means for controlling pressure within aircraftcabins, and relates particularly to means for controlling cabin pressureequipment in a manner which does not impose on the super-chargingequipment undue strain which would limit the flight altitude of theaircraft, and is particularly useful in aircraft using centrifugal cabinsuperchargers.

Superchargers now employed for forcing air into pressure cabins tosupercharge the same must be overspeeded to continue airflow deliverywhen subjected to a compression ratio greatly larger than that for whichthe superchargers have been designed, and if the optimum compressionratio is greatly exceeded, surging of the airflow, interruption of theairflow and overheating of the air will occur.

It is an object of my invention to provide for use with an aircraftpressure cabin, an air pressure control system having a control deviceincorporating means for controlling the cabin pressure with reference tothe compression ratio existing between the exterior and the interior ofthe cabin so that the supercharger will not be forced, even at extremelyhigh altitude flight, to operate against a compression ratio beyond therange in which it will give satisfactory service, thereby making itpossible to maintain the supercharger system in operation throughout theentire altitude range in which the aircraft is capable of flight withoutlimitation by characteristics of the air supply equipment used.

It is a further object, of the invention to provide a cabin pressurecontrol which will avoid the necessity for over speed driving of cabinpressure, air supply equipment when the aircraft is operated abovenormal flight service ceilings. In keeping with the foregoing objects,it is accordingly an object to avoid the necessity for maintainingreserve power for overspeed driving of the cabin pressure air supplyequipment under the conditions expressed in the preceding sentence.

It is a further object of the invention to prevent or avoid seriousairflow reduction or surging of centrifugal and other types ofcompressors employed as an air supply source for pressure cabins, duringoperation at maximum gear ratios.

A further object of the invention is to make possible an importantsaving in weight in cabin pressure air supply systems by placing a knownmaximum value on the compression ratio design requirement and in somecases to eliminate an additional stage of compression in the compressorequipment.

A further object of the invention is to provide an air cabin pressuresystem wherein there is accomplished a limitation of temperature risethrough the air supply blower which is only a function of compressionratio, temperature of the external air, and blower efiiciency.

A further object of the invention is to provide an air control systemfor pressure cabins having means for varying the limiting compressionratio.

A further object is to provide a system of the character Re. 24,990Reissued May 23, 1961 described in the preceding paragraph wherein thelimiting compression ratio is varied in accordance with the temperatureof the outside air. For a supercharger producing a given flow against agiven compression ratio, an increase in the temperature of the air whichlies outside the pressure cabin and which serves as a source of supplyfor the blower makes necessary an increase in supercharger speed inorder to maintain this flow, but in this system higher temperature iscompensated for by a decrease in the compression ratio between theexternal atmosphere and the interior space of the cabin.

A further object of the invention is to provide a simple unit of smallsize and light weight for control of the pressure within an aircraftcabin, this unit incorporating means which will limit the compressionratio to which the blower is subjected in accordance with apredetermined schedule established with relation to the characteristicsand capacity of the blower and its power source.

A further object of the invention is to provide a simple device forlimiting the compression ratio to which the cabin air supply means issubjected, which may be employed with any of the various known or hereinidentified cabin pressure control devices. For example, the pressurelimiting device forming a part of my invention may be used for thecontrol system which held the cabin pressure constant, wherein the cabinpressure is first held constant and is thereafiter maintained at aconstant dilferential over atmospheric, wherein the pressure of thecabin is controlled in accordance with rate of pressure change, whereinthe cabin pressure is a ratio of the ambient external pressure, orcombinations of the foregoing types of pressure cabin control.

A further object of the invention is to provide a system for control ofpressure a pressure cabin, having marked sensitivity to pressure changesby reason of the incorporation therein of an anticipator operativedirectly from changes in the incoming and outgoing flows of air, therebyavoiding lag in control of pressure where this control responds only tochanges in pressure in the cabin, and which system incorporates meansfor limiting the cabin pressure to a value fixed in accordance with apredetermined maximum compression ratio.

A further object of the invention is to provide a system for control ofcabin pressure, having control means responsive to the pressure of airwhich affects the cabin, that is to say, responsive to internalpressure, external pressure or both of them, and means supplementary toor acting directly upon the foregoing control means which willaccomplish a limitation on the maximum pressure diiferential imposed onthe cabin so that the compression ratio against which the superchargermust operate will not exceed a predetermined value.

Further objects and advantages of the invention including mechanisms andcooperative elements whereby the broader objects of the invention may beadvantageously embodied, will be brought out in the following part ofthe specification and the drawings, wherein I have shown electricalmeans for application of energy to move operative parts, withoutlimitation thereto in view of the analogy between electrical andhydraulic power application.

Referring to the drawings which are for illustrative purposes only,

Fig. 1 is a diagrammatic view showing a preferred form of my invention.

Fig. 2 is a diagram or chart for use in explaining characteristics ofthe invention.

Fig. 3 is a perspective view showing an alternative form of mycompression ratio limiting device.

Fig. 4 is a schematic view showing another form of my compression ratiolimiting device.

Fig. 5 is a schematic view showing still another form of my compressionratio limiting device.

Fig. 6 is a schematic view showing a cabin control system whereinobjects of the invention are attained in a reduced assemblage ofcooperating elements.

Fig. 7 is a sectional view showing an alternative form of pressureresponsive regulator which may be used in the system disclosed in Fig.6.

In the preferred form of my invention shown in Fig. 1, 10diagrammatically indicates a pressure cabin having a cabin space 11 intowhich air is fed by air supply means shown as a supercharger or blower12. This blower 12 may be of constant speed or variable speed, but it isto be presumed, for the purpose of this disclosure, that at somerelatively high altitude the blower 12 will be operated at a maximumspeed beyond which the blower will start to surge, overheat, or fail.The cabin is provided with an outlet opening or passage 13 through whichair passes from the cabin space 11 under control of a valve 14 in suchrelation to the inflow of air through the inlet duct 14' that pressureis maintained in the cabin in accordance with a schedule of pressuresand pressure relations under control of the control system, which willnow be described.

Through suitable transmission, here simply shown merely as a shaft 15,the valve 14 is connected to a reversible motor 16 driven in oppositedirections through energization of its windings 17 and 18 so as to closeor open the valve 14.

A power source for driving the motor is shown as a battery 20, one sideof which is connected through a switch 21 to a ground 22. The other sideof the battery is connected through a conductor 23 with contactors 24and 25 of a double pole relay 26 and a composite relay 27. The contactor24 is normally held in an intermediate position, as shown in Fig. l, bysuitable spring means. When the winding 28 of the relay 26 is energized,the contactor 24 will be moved into engagement with the contact 29 of aclosing circuit 30 which includes a contactor 31, connected to thecontactor 25 so as to be moved thereby, and a stationary contact 32which is connected through a limit switch 33 with the outer end of theclosing winding 17 of the motor 16. When the contactor 24 is swung inleftward direction, as the result of energization of the electromagnet34 of the relay 26, it will connect the battery 20 with the contact 35of the opening circuit 36, which extends through a limit switch 37 tothe opening winding 18 of the motor 16. When the electromagnet 38 of therelay 27 is energized, the contactors 25 and 31 thereof will be movedrightward to carry the contactor 31 out of engagement with the contact32, thereby opening the closing circuit 30, and carrying the contactor25 into engagement with a stationary contact39 connected to the openingcircuit 36. Accordingly, when the relay 27 is actuated, it overrides therelay 26, regardless of the position of the contactor 24 of this relay26, and connects the opening winding 18 of the motor 16 through thecontactor '25 with the source of power 20. By suitable energization ofthe windings of the relays 26 and 27, the motor 16 may be actuated toopen and close the valve 14.

The control means shown in Fig. 1 includes a control unit havingpressure responsive elements which are exposed to variable pressures andwhich operate switches associated with the relays 26 and 27. Thiscontrol unit 40 comprises a practically airtight casing 41 which may beconnected through a three-way valve 42 with the cabin space 11 or withan anticipating system 43. This anticipating system 43 includes a duct44 having one end 45 disposed in the air inlet duct 14 and having itsother end 46 exposed in the output passage 13, an intermediate portionof this duct 44 being connected to the three-way valve 42 so that thepressureintermediate the ends of the duct 44 may, by proper setting ofthe valve 42, be transmitted to the interior of the casing. The frontend 45 of the duct 44 is shown as an impact tube and the rear end 46 ofthe duct 44 is shown as a venturi.

4' As previously mentioned herein, a change in the relation of the inletand outlet flows of air through the inlet duct 14' and the outletpassage 13 will produce a change in the pressure in the cabin space, butthis change in pres sure in the cabin space 11 will be relatively slowowing to the large volume of air held therein. The volume of the casing41 of the control unit is quite small and therefore the changes in itsinternal pressure due to pressure changes in the duct 44 of theanticipator system will be comparatively rapid. Why this occurs may beexplained as follows. Air enters the inlet end 45 of the duct 44 at apressure corresponding to the velocity of the air through the duct 14'and leaves the outlet end of the duct 44 at a lower pressure whichvaries with the suction in the venturi 46 resulting from the outlet flowof air through the passage 13. There will be a pressure drop through theduct 44 from the inlet end to the outlet end thereof, and, accordingly,at some intermediate point in this duct, the pressure under normalsteady or stabilized conditions of operation will be the same as thepressure in the cabin space 11, but should the relative flows of airthrough the duct 14' and outlet 14 be changed from their existingvalues, there will be an immediate change in pressure transmittedthrough the anticipator system 43 to the casing 41. Should the point ofconnection of the casing 41 be closer to one end of the duct 44 than theother, or should the friction head of the ducts on the opposite sides ofthe point of connection be unbalanced, a balancing orifice 47 may beinserted at a suitable point in the duct 44. For the purpose of furtherdisclosure of the invention, it may be assumed that the pressureexisting'in the casing 41 of the unit 40 is cabin pressure. On the otherhand, it may be made in fact exactly cabin pressure by adjusting thethree-way valve 42 so that it will connect the cabin space 11 directlywith the interior of the casing 41. Within the casing 41 there is aconstant pressure control element 48 comprising an aneroid 49 whichmoves a control member 50 in accordance with changes in pressure in thecasing 41. This member 50 comprises a moving contactor hinged at 51 andbeing electrically grounded as at 52. On opposite sides of the free endof the member 50 there are contacts 53 and 54 which may be respectivelyreferred to as the opening and closing contacts. These contacts 53 and54 may be adjustably mounted, as by means of'a vertically adjustableblock 54, so that they may be moved upwardly or downwardly from theposition in which they are shown, whereby control will be exercised withreference to other cabin pressures than those which will be hereinreferred to for the purpose of explanation. The contacts 53 and 54 maybe positioned so that when the pressure in the casing 41 is at aselected value, for example, 22 inches Hg, the contactor 50 will lie inan intermediate position between them. Should pressure within the casing41 then increase, the aneroid 49 will be reduced in vertical dimensionand the contactor 50 will be moved downward into engagement with thevalve opening contact 53, whereupon current will be fed through aconductor 55 to energize the electromagnet 34 of the relay 26 and movethe contactor 34 into engagement with the contact 35, whereupon thewinding 18 of the motor 16 will be energized, to rotate the motor in adirection to open the valve 14 and thereby increase the rate of airoutflow through the passage 13.

Returning now to the control unit 40, should there be a drop in pressurewithin the casing 41, expansion of the aneroid 49 will move thecontactor 50 into engagement with the closing contact 54 and the currentwill be fed through a conductor 56 to the electromagnet 28 of the relay26, moving the contactor 24 into engagement with the contact 29 toenergize the winding 17 of the motor, whereupon a closing movement ofthe valve 14 and a restriction of the outflow of air from the cabinspace 11 will be accomplished.

To override the action of the control 48, when the aircraft rises. abovethe elevation for which the control 48 'the contact 68.

is adjusted, I provide a pressure difier'ential control 57 comprising amember 58 which is responsive to the pressure differential existingbetween the interior and the exterior of the cabin 10. This member 58comprises a capsule, the exterior of which is exposed within the casing41 and the interior of which is connected through a duct 59 with ambientflight pressure exterior of the cabin 10. The movable wall of thiscapsule 58 is connected through a suitable link with a contactor arm 60hinged at 61 and electrically grounded as indicated at 62. Above thefree end of the contactor 60 there is a contact 63, which may beadjustably mounted, but which is so positioned with relation to thecontactor 60 that it will be engaged by the arm 60 when the pressuredifierential between the cabin interior and the outside atmospherereaches a prescribed value determined in accordance with factorsincluding the strength of the cabin shell. When this occurs, currentwill flow from the contactor 60 through the override circuit 64 to theoverride relay 27, energizing the electromagnet 38 thereof so that thecontactors 25 and 31 will be moved rightward from the positions in whichthey are shown, this movement energizing the winding 18 of the motor 16as previously described with relation to the action of the overriderelay 27.

The control unit 40 also includes a compression ratio control means 65which is responsive to variations in absolute cabin pressure andvariations in ambient flight absolue pressure exterior to the cabin. Thecontrol means 65 has a contactor lever or arm 66 grounded as indicatedat 67 and adapted to engage a stationary or adjustable contact 68. Thiscontactor arm 66 is movable by means 69 which is actuated by absoluteambient flight pressure, and by an element 70 which is actuated byabsolute cabin pressure or the simulated substantial equivalent thereofrepresented by the pressure in the casing 41 of the unit 40. The element69 comprises an evacuated capsule 71 in axial alignment with a capsule72 having its exterior exposed to the pressure within the shell 41 andits intcrior connected to ambient flight pressure through a tube 73which connects to the duct 59. The element 70 comprises an evacuatedcapsule or aneroid mounted within the casing 41 and expanding andcontracting in accordance with changes in the absolute pressure existingwithin the casing 41. The upper end of the contactor arm 66 is connectedbetween the capsules 71 and 72 of the means 69 and an intermediateportion of the arm 66 is connected to the capsule 70.

The contact 68 is positioned with relation to the lower end of thecontactor arm 66 with regard to the limiting pressure differential underwhich the pressure system of the aircraft cabin is to operate.Accordingly, when this compression ratio is below the selected limitingvalue, the movable contactor arm is out of engagement with the contact68. An increase in cabin pressure will reduce the axial dimension of thecapsule 70 and thus carry the lower end of the arm 66 toward the contact68. Likewise, a reduction in the pressure outside the aircraft cabinwill be transmitted through the duct 59 to the interior of the capsule72, causing the same to decrease in size, thereby moving the upper endof the arm 66 in counterclockwise direction so that its lower end willbe moved toward When the compression ratio limit is reached, the lowerend of the contactor arm 66 will have been moved into engagement withthe contact 68 so that current will be caused to flow through aconductor 69' which connects with the electromagnet 38 of the relay 27.This will result in energization of the winding 18 of the motor 16 sothat the valve 14 will be opened to permit an increase in the rate offlow of air from the cabin space, thereby reducing the absolute cabinpressure to which the compression ratio control 65 is subjected. Theeffect of the foregoing is to prevent the compression ratio of thepressure in the cabin space 11 to the pressure in the space external tothe cabin from exceeding a predetermined value within which suitableoperation of the blower 12 is obtainable.

The invention includes means for lowering the compression ratio inresponse to rise in temperature of the external air, comprising meansfor relative adjustment of the contactor 66 and the capsule 70. Thisrelative adjustment is accomplished by movement of the capsule 76 towardand away from the capsule 71 in response to changes in temperature inthe external air. The capsule 70 is connected to a plunger 75 extendinginto a cylinder 76 connected by a fluid filled tube 77 with a fluidfilled chamber 78 exposed to temperatures existing outside the aircraftcabin. The expansion and contraction of the fluid in the chamber 78 istransmitted through the tube 77 to the cylinder 76 wherein it acts tomove the plunger 75 and the capsule 70 in accordance with the rise andfall of outside temperature.

The operation of the invention may be explained with relation to thechart shown in Fig. 2, wherein the length of the horizontal line O--Erepresents a change in altitude from zero or sea level to 40,000 feetand the line O-P is laid off to indicate the corresponding atmosphericpressure in inches of Hg. On this chart we have indicated atmosphericflight altitude-pressure relation, or, in other words, thealtitude-pressure relation of the normal external atmosphere. In Fig. 2I have also indicated a differential pressure curve such as would bemaintained by the differential control 57, and a compression ratio curvesuch as produced by the operation of the compression ratio control 65.When the flight of the aircraft is started from a low level, forexample, substantially sea level, the pressure in the cabin as seen fromthe graph, Fig. 2, will be around 30 inches Hg and at this time thecontactor 50 will be in engagement with the valve opening contact 53. Ifthe switch 21 is then closed so as to energize the electrical system,the motor 16 will be operated to open the outlet valve 14 to its fullestextent whereupon operation of the motor will be stopped by the openingof the limit switch 37. Since the disclosure is diagrammatic, themechanical connection of the limit switches 33 and 37 with the shaft 15of the motor has not been shown, especially since the use of limitswitches with electrically driven parts is well known. It will beunderstood that any known means for opening the limit switches 33 and 37at the ends of the range of movement of the valve 14 may be employed.

As the ship climbs, there will be a gradual reduction in atmosphericpressure, which reduction in pressure will be duplicated within thecabin space .11 for the reason that at this time the blower 12 is merelycirculating air through the cabin. As an altitude of about 8,000 feet isapproached, the reduction in pressure within the casing 41 will resultin an expansion of the aneroid 49 to lift the contactor 50 fromengagement with the contactor 53 into engagement with the contact 54 andthe constant pressure control 48 will then act to operate the electricalsystem associated with the motor 16 in such manner that the valve 14will be gradually closed as upward flight continues, thereby maintainingin the cabin space a constant pressure of about 22 inches Hg until thediiferential control 57 comes into operation, as indicated by thehorizontal line A-C of Fig. 2. The action of the differential control 57will be to control the override switch 27 so as to accomplish an openingof the outlet valve 14 to produce a drop in the cabin pressure asindicated by the line C-D of Fig. 2, forming a short section of thedifierential pressure curve. As the flight altitude corresponding to thepoint D is reached, the contactor arm 66 of the compression ratiocontrol will be moved into engagement with the contactor 68, whereuponcontrol of the override switch 27 will be exercised by the compressionratio control means 65 to countervail the action of the control 54 andthe cabin pressure will be maintained at the values indicated by thatportion of the compression ratio curve lying to the right of the pointD, during further increase in the flight altitude of the craft.

Should the compression ratio control 65 be adjusted so as to establish arelatively low compression ratio limit, such as represented by thecompression ratio curve in Fig. 2, the difierential pressure control 57may be disconnected from the system by the opening of the switch 79 inthe conductor 64. Then the constant pressure control 48 will control thecabin pressure as indicated by the line A-F until the compression ratiolimit indicated by the compression ratio curve is reached, at which timethe control will be taken over by the compression ratio control means 65which will thereafter countervail any control sought to be activated bythe element 48. Also, the constant pressure control 48 may be set, as byraising the contacts 53 and 54 from the positions in which they areshown, so that the compression ratio control will not start to functionuntil the altitude indicated at B is reached, with a correspondingpressure of about 19 inches Hg. The constant pressure control will thenbe maintained as indicated by the line BG until the compression ratio isreached at the point G, control of the cabin pressure then being takenover by the compression ratio control 65, without any use of thedifierential pressure control 57.

In Fig. 3, I show an alternative form of my compression ratio controldevice which is intended to replace the compression ratio control device65. This alternate form of the device comprises a member 81 which isresponsive to cabin pressure changes and a member 82 which is responsiveto flight altitude pressure changes. The members 81 and 82 are bothaneroids comprising hollow metal bodies which are expansible andcontractible axially. These hollow bodies, and also the other aneroidsshown in the drawings, are contracted by evacuation, against the springaction of the metal walls thereof tending to resist contraction, oragainst spring means applied for this purpose.

The aneroid 81 is exposed to cabin pressures so that it will expand asthe pressure within the cabin decreases. The aneroid 82 is exposed toambient flight pressure so as to expand in accordance with reduction inexternal atmospheric pressures. The aneroids 81 and 82 lie on oppositesides of a wall 83 through which a shaft 84 extends, this shaft 84extending through an opening 85 in the wall which is of such size thatthe leakage therethrough will be very small. One portion of the shaft 84is connected to the top of the aneroid 82 by means of a bi-metalliethermostatic arm 86. The portion of the shaft 84 lying on the oppositeside of the wall 83 supports a fulcrum arm 87 having the forward portion88 thereof connected to the aneroid 81. The movement of the fulcrum arm87 is an index of the changes in or existing compression ratio effectivebetween the exterior and the interior of the cabin. Its changes inposition may be used to control the operation of the airflow equipmentof the pressure cabin in exactly the same manner as does movement of thecontactor arm 66 in the earlier described embodiment of my compressionratio control device. A simple method of doing this is to employ the arm87 as part of a switch, and accordingly I have shown the arm 87 groundedat 89 so that it will serve as a contactor to engage a contact 90connected by a conductor 91 with switch means 92. The chamber 93containing the aneroid 82 receives a continuous flow of external airthrough inlet and outlet pipes 94 and 95. Accordingly, the temperaturein this chamber 93 changes in accordance with the temperature of the airexterior of the aircraft and the bi-metallic arm 86 flexes in accordancewith these changes in temperature and modifies the compression ratio inaccordance with temperature changes.

In the compression ratio control shown in Fig. 4 which again is to takethe place of control device 65, I provide a small evacuated chamber 96having therein resilicut capsules 97 and 98 connected through means 99with a switch lever 100, so that the action of the capsules 97 and 98will be to move the switch lever 100- in opposite directions. Thisswitch lever 100 is hinged at 101 and is grounded as indicated at 102. Acontact 103 is disposed adjacent the swinging end of the lever 100 so asto be engaged by this lever when it is moved in the direction of thecapsule 97. The capsule 97 is connected through a tube 104 with ambientflight pressure and the capsule 98 is connected through a tube withcabin pressure. The capsules 97 and 98 expand and contract in accordancewith and under control of the changes in flight and cabin absolutepressures, and the arm 100 is moved through positions corresponding tothe compression ratio or, in other words, the ratio of the absolutepressures to which the chambers of the capsules 97 and 98 are subjected.

The form of compression ratio control shown in Fig. 5 is similar to theone shown in Fig. 4, in that it has an evacuated shell 96', but dilfersin the provision of capsules 97 and 98 in side by side or parallelrelation. These capsules 97' and 98' are respectively connected throughducts 104' and 105' with ambient flight pressure and cabin pressure. Themovable walls of these capsules 97' and 98 are connected to spacedpoints of a contactor lever 110. A decrease in ambient flight pressureor an increase in cabin pressure will cause the free end 111 to movedownward toward the contact 112 associated with an electrical controlcircuit. The position of the lever at any time corresponds to theexistent compression ratio, and the contact 112 is placed so that itwill be engaged when a prescribed compression ratio limit is reached. Itwill be understood that temperature compensation means may be applied todevices shown in Figs. 4 and 5 in accordance with the teachings found inFigs. 1 and 3.

In the form of the invention previously described, the compression ratiolimitation has been accomplished by use of an instrument independent ofthe cabin pressure regulator, making it possible to vary the cabinpressure regulation without such regulation affecting the compressionratio control instrument. In Fig. 6, I show a form of my inventionwherein the compression ratio limitation is accomplished by meanssupplementary to the cabin pressure regulator when it is designed orfactory adjusted to operate at predetermined values.

In Fig. 6 those parts which are the same as previously shown in Fig. 1will be referred to by the same numbers. Within the cabin space 11 thereis a control unit 40 having a casing 41' having at the rightward endthereof a constant pressure regulator 48 comprising an aneroid 49mounted on a bracket 100' to which a contactor 50 is hinged. Through alink 101, the expansion and contraction of the aneroid 49, in responseto differences in pressure in the chamber 102', will swing the contactor50 back and forth between opening and closing contacts 53 and 54adjustably mounted for lateral movement by means of insulators 103'. Thechamber 102' receives anticipated cabin pressure variations by reason ofits connection through a duct 104' with the anticipator system 43. Thecontactor 50 is energized through a conductor 105' only when thecontactor 60 of the differential pressure regulator 57 is in loweredposition so as to engage a contact 106 to which one end of the conductor105 is connected, the contactor 60 then connecting a ground 62 with thecontactor 50 through the contact 106 and the conductor 105'.Accordingly, prior to the time the differential pressure control comesinto operation as the result of the expansion of its capsule 58, thecontactor 50 of the cabin pressure constant control 48 will be connectedwith the ground, and by contact with either of the contact 53 or 54,will complete circuits 55 and 56 through either the electromagnet 34 orthe electromagnet 28 of the double pole relay 26, these circuits beingcompleted through a conductor 107 extend- 9. ing to a low voltage powersource such as a battery E08 which is connected through the switch 21with the ground 19. Accordingly, the movement of the contactor 50' aspreviously described will energize the relay 26 so that either theopening circuit 36 or the closing circuit 37 associated with the motor16 will be energized fuom the power source 20 as the result of thecontactor 24 being moved into engagement with the respective contacts 29and 35 of the relay 26.

The contactor 60 is carried by a hinge 61' placed intermediate its ends,and when the pressure drop of the ambient atmosphere transmitted to thechamber 110 of the casing 41' through a duct 111', or a rise in thepressure within the capsule 58 lifts the contactor 60, the contactor Iwill be disconnected from the ground so that the constant pressurecontrol 48 will be no longer energized. Expansion of the capsule 58 willmove the contactor 60 into engagement with the contact 112' which isconnected through a conductor 113 with an electromagnet 34 of the relay26. This will cause a leftward swinging of the contactor 24 so that theopening circuit 36 of the motor 16 will be energized.

During the operation of the differential control 57, there will be agradual expansion of an aneroid 115 in accordance with the reduction inambient flight pressure transmitted through the duct 111' to the chamber110'. This aneroid 115 is disposed above and in cooperative relation tothe rightward end of the lever forming the contactor 60, and when thecompression ratio limit is reached, the downward force of the aneroid115 will supplement the upward force of the capsule 58, so that thecontactor 60 will then act in cooperation with the contact 112'.

The aneroid 115 has associated temperature responsive control meansshown as a fluid filled bellows 118 acting as a means for connecting theaneroid 115 to an adjustable support 119 having a screw 120 whereby theassembly of bellows 118 and aneroid 115 may be moved vertically, andalso having a laterally slidable base 121 for lateral adjustment of theassembly. The bellows 118 is connected through a tube 122 with a gas orliquid filled tube or bulb 123 disposed so that it will be affected bytemperature of external air. To provide enhanced sensitivity, thebellows 58 of the dilfercntial pressure control 57 is connected througha duct 124 with the anticipator system 43 at a point near the outletventuri 125 to which the outlet end of the anticipator duct 44 isconnected.

In the operation of the device shown in Fig. 6 pressure control isaccomplished which may be readily explained with relation to the chartFig. 2. When the aircraft is at an altitude below the point A, thecapsule 58 will be relatively compressed or collapsed and therefore thecontactor 60 will be in engagement with the contact 106. Also, theaneroid 49 of the constant pressure control will be collapsed and thecontactor 50 thereof will be in engagement with the contact 53, with theresult that the relay 26 will be energized so as to close the openingcircuit 36 associated with the motor 16 and the outlet valve will beopen.

As the flight altitude is increased toward the point A, the aneroid 49will gradually expand so that at the point A the contactor 50 will bemoved rightward into engagement with the contact 54 thereby actuatingthe electrical control so as to operate the motor in a manner togradually close the outlet valve and maintain the cabin pressuresubstantially constant as indicated by the line A-C. When the point C isreached, the expansion of the capsule 58 will have caused lifting of thecontactor 60 into engagernent with the contact 112, whereupon thecontrol of the cabin pressure will be then by the differential pressurecontrol 57, and this differential control will be maintained asindicated by the line C-D between the respective flight altitudesthereby indicated. At the flight altitude D, expansion of the aneroid115 will have accomplished pressural engagement thereof with therightward or rear end of the contactor 60, this supplementarypressurqthen causing the cabin control to follow approxh matcly alongthe compression ratio curve rightward from the point D by countervailingany control action of the difierential pressure control 57 which wouldlend to close the valve 14 with a resultant increase in cabin pressure.

In Fig. 7, I show another means whereby the compression ratio limitationcan be added to the cabin regulator, thereby avoiding use of a separatecompression ratio control such as shown in Fig. l. The control unitshown in Fig. 7 may be substituted in the system shown in Fig. 6 for thecontrol unit 40'. It has contacts 53, 54, 106, and 112' which areconnected into the electrical system of Fig. 6 in the manner showntherein. The casing of the unit shown in Fig. 7 has a port whereby itsinterior may be connected through the duct 104' of Fig. 6 with theanticipator system 43, the duct 124 being entirely omitted. The casinglikewise has a port 131 for connection with the duct 111 which will thentransmit ambient flight pressure to the capsule 58' which moves acontactor arm 60' between contacts 106 and 112', thereby controlling thecabin pressure in accordance with dilferential in its proper sequence,as will be brought forth hereinafter. Within the casing of the unitthere is an aneroid 49' which moves the contactor arm 50' betweencontacts 53 and 54- so as to produce a constant pressure control of thecabin altitude or internal atmosphere in the same manner as thecontactor arm 50 of Fig. 6. It will be noted that the contact 106 isconnected through a conductor 105' with the contactor arm 50', so thatthis arm will not be connected to ground 62' when the contactor 60 ismoved from engagement with the contact 106 as the result of the increasein the pressure differential acting externally of the capsule 58' whichcorresponds to the capsule 58 of Fig. 6, with the exception that in Fig.7 the interior of the capsule is exposed to ambient flight pressure andthe exterior is exposed to cabin pressure through the anticipatorsystem, in reverse of Fig. 6.

When flight altitude is below the value A, Fig. 2, the contactor arm 60'will be in engagement with the contact 106 and the collapsed conditionof the aneroid 49' will hold the contact arm 50' in engagement with thecontact 53, the result being that the outlet valve will be maintained inopen position. As the altitude A is reached, reduction in cabin pressurewill result in expansion of the aneroid 49' and the contactor arm 50will be moved toward the contact 54 and by cooperation with the contact54 a constant cabin pressure will be maintained, as indicated by theline A-C of Fig. 2. At the point C of Fig. 2, the contactor arm '60 willmove away from the contact 106 and will thereafter cooperate with thecontact 112' to control the cabin at the differential pressure C-D. Thecontactor arm 50' is characterized by flexibility or yieldability sothat as the flight altitude rises, the expansion of the aneroid 49' willflex the intermediate portion of the contactor arm 50' rightward afterthe lower end thereof engages the contact 54. The result of thiscontinued flexure is that a projection 135 on the contactor arm 50' willengage a projection 136 which is carried by the contactor arm 60', sothat expansion of the aneroid 49', when the point D is reached, willtransmit pressure through the projection 135 to the contactor arm 60',to supplement the action of the capsule 58' and produce a control ofcabin pressure along the compression ratio curve of Fig. 2 rightwardfrom the point D.

The interconnection between the aneroid 49' and the contactor arm 60'embraces a regulation responsive to external temperature variations.This regulation is shown as an expansible fluid filled bellows 137forming a part of the projection 136, this bellows being connectedthrough a flexible tube 138 with a port 139 which may be connected tothe tube 122 leading to the tube or bulb 123 shown in Fig. 6.Accordingly, the temperature of the external air rises, an expansion ofthe bellows 137 is produced so that cooperation of the aneroid 49' toproduce compression ratio control occurs at a lower point in the flightaltitude, with the result that the compression ratio limit is reducedfrom its previous value.

The casing of the device shown in Fig. 7 has a cover 143 carrying on itsinner face brackets 140 and 141 for carrying the active parts of theinstrument; thereby it is possible by removal of the cover to remove theoperating parts of the device from the casing.

I claim as my invention:

1. In a system for air-supercharging a cabin, the combination of:supercharging means for the cabin com.- prising means for delivering aflow of air into the cabin and emitting a flow of air from the cabin,the relative values of these flows determining the pressure Within thecabin; means for controlling the operation of said supercharging meanscomprising means responsive to the pressure of air affecting said cabinto control said supercharging means through a range of externalpressures to which said cabin is exposed; a compression ratio controlhaving a part movable through consecutive positions representative ofconsecutive compression ratios, means operating in response to changesin absolute pressure vn'thin said cabin to apply a force to move saidpart, and in cooperating therewith means operating in response toabsolute pressure outside said cabin to apply a force to move said part;and means whereby said movable part effects control of said controllingmeans so that the pressure of air in said cabin will at no time exceed apredetermined multiple of the absolute pressure of air outside saidcabin.

2. In a device for air-supercharging an aircraft cabin, the combinationof: air supply means for delivering a flow of air under pressure intothe interior of the cabin; variable flow outlet means for emitting airfrom the interior of the cabin; motivating means to actuate said outletmeans, said motivating means including a source of energy which isutilized to operate the motivating means; means acting in response tochanges in air pressure affecting said cabin to control the applicationof said energy in said motivating means; a pressure change sensitiveelement movable in response to changes in absolute pressure within saidcabin; a pressure change sensitive element movable in response tochanges in ambient absolute pressure; a member receiving movement fromsaid elements in such manner that its movement is in accordance withchanges in the ratio of the absolute pressures within and outside saidcabin; and means operated by said member for controlling the applicationof energy in said motivating means to actuate said outlet means so thatthe absolute pressure within said cabin will be maintained within thelimits of a fixed proportion of the ab solute pressure exterior of saidcabin.

3. In a system for air-supercharging an aircraft cabin, the combinationof: air supply means for delivering a flow of air into the interior ofthe cabin; variable flow outlet means for emitting air from the interiorof the cabin; motivating means to actuate said outlet means, saidmotivating means including a source of energy which is utilized tooperate the motivating means; means acting in response to changes in airpressure aflecting said cabin means; means responsive to absolutepressure within said cabin and absolute pressure exterior thereofcontrolling the application of energy in said motivating means toactuate said outlet means so that the absolute pressure within saidcabin will be maintained within the limits of a fixed proportion of theabsolute pressure exterior of said cabin; and means responsive to thetemperature of air exterior of said cabin for varying the action of saidmeans responsive to absolute pressure to vary said proportion.

4. In a system for air-supercharging an aircraft cabin, the combinationof: air supply means for delivering a flow of air into the interior ofthe cabin; variable flow outlet means for emitting air from the interiorof the '12 cabin;'motivating means to actuate said outlet means, saidmotivating means including a source of energy which is utilized tooperate the motivating means; means acting in response to changes in airpressure affecting said cabin to control the application of said energyin said motivating means; an element movable in response to changes inabsolute pressure within said cabin; an element movable in response tochanges in absolute pressure outside said cabin; a member receivingmovement from said elements in such manner that its movement is inaccordance with changes in the ratio of the absolute pressures withinand outside said cabin; means operated by said member for controllingthe application of energy in said motivating means to actuate saidoutlet means so that the absolute pressure within said cabin will bemaintained within the limits of a fixed proportion of the absolutepressure exterior of said cabin; and means responsive to the temperatureof air exterior of said cabin for varying the action of said meansresponsive to absolute pressure to vary said proportion.

5. In a system for air-supercharging a cabin, the combination of:supercharging means for the cabin comprising means for delivering a flowof air into the cabin and emitting a flow of air from the cabin, therelative values of these flows determining the pressure within thecabin; means for controlling the operation of said supercharging meanscomprising means responsive to the pressure of air afiecting said cabinto control said supercharging means through a range of externalpressures to which said cabin is exposed, and means responsive toabsolute pressure inside and outside said cabin to limit the action ofsaid supercharging means so that the absolute pressure of air in saidcabin will not exceed a predetermined multiple of the absolute pressureof air outside said cabin; and means responsive to changes intemperature for changing the value of said predetermined multiple.

6. In a device for air-supercharging an aircraft cabin, the combinationof: air supply means for delivering a flow of air under pressure intothe interior of the cabin; variable flow outlet means for emitting airfrom the interior of the cabin; motivating means to actuate said outletmeans, said motivating means including a source of energy which isutilized to operate the motivating means; means acting in response tochanges in air pressure affecting said cabin to control the applicationof said energy in said motivating means; and a control means comprisingan aneroid responsive to absolute pressure inside said cabin and ananeroid responsive to absolute pressure outside said cabin operativelyinterconnected to control the application of energy in said motivatingmeans to actuate said outlet means so that the absolute pressure withinsaid cabin will be maintained within the limits of a fixed proportion ofthe absolute pressure exterior of said cabin.

7. In a system for air-supercharging an aircraft cabin, the combinationof: air supply means for delivering a flow of air into the interior ofthe cabin; variable flow outlet means for emitting air from the interiorof the cabin; motivating means to actuate said outlet means, saidmotivating means including a source of energy which is utilized tooperate the motivating means; means acting in response to changes in airpressure affecting said cabin to control the application of said energyin said motivating means; a control comprising an aneroid responsive toabsolute pressure inside said cabin and an aneroid responsive toabsolute pressure outside said cabin controlling the application ofenergy in said motivating means to actuate said outlet means so that theabsolute pressure within said cabin will be maintained within the limitsof a fixed proportion of the absolute pressure exterior of said cabin;and means responsive to the temperature of air exterior of said cabinfor varying the action of said means responsive to absolute pressure tovary said proportion.

8. In a system for air-supercharging a cabin, the combination of:supercharging means for the cabin comprising means for delivering a flowof air into the cabin and emitting a flow of air from the cabin, therelative values of these flows determining the pressure within thecabin; and means for controlling the operation of said superchargingmeans comprising means responsive to the pressure of air atfecting saidcabin to control said supercharging means through a range of externalpreslures to which said cabin is exposed, and incorporating meansresponsive to absolute pressure inside said cabin to override said meanswhich is responsive to pressure of air affecting said cabin andeffectuate such control of said supercharging means so that the absolutepressure of air which it maintains in said cabin will not exceed apredetermined ratio of the absolute pressure of air outside said cabin,said means responsive to absolute pressure also having means for varyingsaid ratio in accordance with the variations of temperature of the airoutside said cabin.

9. In a system for air-supercharging a cabin, the combination of: airsupply means for delivering air into the interior of the cabin from asource of air; outlet valve means adapted to be relatively opened andclosed so as to vary the pressure of air in said cabin; opening powermeans actuatable to open said valve means; closing power meansactuatable to close said valve means; compressionratio control meansoperative to actuate said opening power means whenever the absolutepressure in said cabin reaches a predetermined multiple of the absolutepressure of said source of air; means acting in response to changes intemperature of the air forming a part of said source of air to changethe value of said predetermined multiple; and control means operatingwhen said absolute pressure in said cabin is below said predeterminedmultiple to actuate said power means in response to changes in pressureof air affecting said cabin.

1-0. In an aircraft adapted to be supercharged, blower means forsupplyingair to a pressure tight cabin, control means for regulating therate of air discharge from the cabin so as to control the pressuremaintained therein, pressure regulator means adapted to controllablymaintain pressure within said cabin below a predetermined pressurealtitude, and secondary regulator means operating in response to thecompression ratio existing between the air inside the cabin and the airoutside the cabin approaching a value which would impair the chiciencyof said blower means to override the action of said primary pressureregulator means and regulate the rate of air discharge from the cabinwhereby the pressure of air within the cabin will be maintained withinthe limits of a maximum value wherein eflicient operation of said blowermeans is obtainable.

1 1. In a cabin pressure regulator adapted to limit cabin pressure alonga predetermined value of the absolute compression ratio, three pressuresensitive capsules, two of which are interconnected by means of joinderin tandem position with their outer ends fixed, these joint capsulesconsisting of one aneroid exposed to cabin pressure and a differentialpressure capsule subjected to flight pressure and cabin pressure, thethird capsule consisting of an aneroid exposed to cabin pressure andadjustable in its mounted position, a control operating member hinged tothe third capsule and to said tandem capsules at a point contiguous tosaid means of joinder, and switch means adapted to be actuated by saidmember whenever a predetermined cabin compression ratio with respect toflight pressure is exceeded.

12. In a cabin pressure regulator adapted to limit cabin pressure alonga predetermined value of the absolute compression ratio, three pressuresensitive capsules, two of which are interconnected by means of joinderin tandem position with their outer ends fixed, these joint capsulesconsisting of one aneroid exposed to cabin pressure and a differentialpressure capsule subjected to flight pressure and cabin pressure, thethird capsule consisting of an aneriod exposed to cabin pressure andadjustable in its mounted position, and a control operating member 14hinged to the third capsule and to said tandem capsules at apointcontiguous to said means of joinder.

13. In an aircraft cabin adapted to be supercharged, a blower means forsupplying air under pressure to said cabin, a valve means interposed inthe wall of said cabin to vary the rate of air discharge of said cabin,a regulator means adapted to control pressure through controlling theaction of said outlet valve, said regulator means comprising aneroidmeans responding to pressure within the cabin to control cabin pressureat a predetermined constant value, a differential pressure capsulesubjected to cabin pressure and flight pressure arranged to overridesaid aneroid means when a predetermined cabin differential pressure isexceeded, and a second aneriod means subjected to ambient flightpressure and adapted to coact with said differential pressure capsule toreduce the limiting value of differential pressure whenever saidaircraft is flown above a predetermined flight altitude, the saidinfluence on the diflerential pressure limit being such that cabinpressure is limited to and controlled along a schedule practicallyconforming to a predetermined ratio of the absolute pressures in thecabin with respect to flight altitude pressure.

14. In an aircraft cabin adapted to be supercharged, a blower means forsupplying air under pressure to said cabin, a valve means interposed inthe wall of said cabin to vary the rate of air discharge of said cabin,a regulator means adapted to control pressure through controlling theaction of said outlet valve, said regulator comprising aneroid meansadapted to control cabin pressure at a predetermined constant value, adifferential pressure capsule subjected to cabin pressure and flightpressure arranged to override said aneroid means when a predeterminedcabin pressure ditferential is exceeded, and a second aneroid meanssubjected to flight pressure and adapted to influence said difierentialpressure capsule to reduce the limiting value of diflerential pressurewhenever said aircraft is flown above a predetermined flight altitude,the said influence on the differential pressure limit being such thatcabin pressure is limited to and controlled along a schedule practicallyconforming to a predetermined ratio of the absolute pressures in thecabin with respect to flight altitude pressure; and means responsive totemperature to vary the value of said predetermined ratio.

15. In an aircraft cabin adapted to be supercharged, a blower means forsupplying air under pressure to said cabin, a valve means interposed inthe wall of said cabin to vary the rate of air discharge of said cabin,a regulator means adapted to control cabin pressure through the actionof said outlet valve to said regulator comprising an aneroid adapted tocontrol cabin pressure at a predetermined constant value, a diiferentialpressure capsule subjected to cabin pressure and flight pressurearranged to override said aneroid when a predetermined cabin pressuredifferential is exceeded, said aneroid being arranged adjacent saiddiiferential pressure limiting means so that expansion of the aneroidwhen cabin pressure is reduced below a predetermined value will impose areduction in the limiting diiferential pressure whereby cabin pressureis limited to and controlled along a schedule practically conforming toa predetermined ratio of the absolute pressures in the cabin withrespect to flight; and means operating in response to changes intemperature to vary the value of said predetermined ratio.

16. Mechanism to control ventilation through and pressure within anaircraft cabin whereinto air is supplied under pressure, comprisingmeans to control the flow of air through the cabin, absolute-pressuresensitive means operatively connected thereto to maintain cabin pressuresubstantially constant throughout a medium altitude range,difierential-pressure sensitive means also operatively connected theretoto maintain a substantially constant differential of cabin pressure overatmospheric pressure throughout a higher altitude range, and meansoperable in accordance with a selected ratio between cabin absolutepressure and atmospheric pressure, also operatively connected to theflow-controlling means, to maintain such ratio substantially constantthroughout the highest altitude range.

17. In an aircraft cabin adapted to be supercharged; a blower means forsupplying air under pressure to said cabin; a valve means interposed inthe wall of said cabin to vary the rate of air discharge of said cabin;a regulator means adapted to control cabin pressure through the actionof said outlet valve; said regulator comprising an aneroid responsive tochanges in pressure within the cabin operable to regulate said valvemeans to control cabin pressure at a predetermined constant value; and adifferential pressure capsule responsive to the difference between cabinpressure and atmospheric pressure operative to override the control ofsaid aneroid when a predetermined cabin differential pressure isexceeded; said aneroid being arranged adjacent to said differentialpressure capsule whereby expansion of the aneroid, when cabin pressureis reduced below a predetermined value will, progressively limit theaction of said differential pressure capsule to increase cabin pressure,thereby progressively decreasing the cabin differential pressure as thecabin absolute pressure decreases to maintain the cabin absolutepressure in accordance with a predetermined ratio between cabin absolutepressure and atmospheric absolute pressure.

18. Mechanism to control ventilation through and pressure within anaircraft cabin whereinto air is continually supplied under pressure,comprising: an outflow valve normally open at all altitudes; and threedevices operatively connected to the valve to regulate its openingthrough three different altitude ranges, said devices comprising,respectively, an absolute-pressure sensitive means tending to maintainconstant cabin pressure throughout a medium altitude range, adifferential-pressure sensitive means tending to maintain a constantdifferential of cabin pressure over atmospheric pressure throughout ahigher altitude range, and a ratio-sensitive means tendingto maintain aconstant ratio between cabin pressure and atmospheric pressurethroughout the highest altitude range.

19. Mechanism to control ventilation through and pressure within anaircraft cabin whereinto air is continually supplied under pressure,comprising: means to effect and control outflow from the cabin; and atleast two means operatively connected to the outflow-controlling meansto regulate outflow; the first of said regulating means being responsiveto cabin pressure and operable to effect elevation of cabin pressureover atmospheric pressure; and the second being operable in accordancewith a selected ratio of cabin pressure to atmospheric pressure, andarranged to override the first regulating means to regulate cabinpressure in accordance with such ratio.

20. Mechanism to control ventilation through and pressure within anaircraft cabin whereinto air is continually supplied under pressure,comprising: means to effect and control outflow from the cabin; and atleast two means operatively connected to the outflow-controlling meansto regulate outflow; the first of said regulating means being responsiveto cabin pressure and operable to maintain the cabin pressuresubstantially constant; and the second being operable in accordance witha selected ratio of cabin pressure to atmospheric pressure, and arrangedto assume control over all other regulating means to regulate cabinpressure in accordance with such ratio.

21. Mechanism to control ventilation through and pressure within anaircraft cabin whereinto air is continually supplied under pressure,comprising: means to effect and control outflow from the cabin; and atleast two means operatively connected to the outflow-controlling meansto regulate outflow; the first of said regulating means being operablein accordance with the differential of cabin pressure over atmosphericpressure, to maintain such differential substantially constant; and thesecond being operable in accordance with a selected ratio of cabinpressure to atmospheric pressure, and arranged to override all otherregulating means to regulate cabin pressure in accordance with suchratio.

22. In combination with a substantially airtight aircraft cabin ofselected resistance to bursting, and having an outflow port; a blower ofselected compression ratio connected for continual supply of air underpressure within the cabin; valve means controlling outflow from andhence pressure within the cabin; and at least two means operativelyconnected to the valve means to regulate cabin pressure; one of saidregulating means being sensitive to the differential of cabin pressureover atmospheric pressure, and always active to prevent the attainmentof a differential in excess of the selected bursting stress, within agiven margin of safety; and the other of said regulating means beingoperable to regulate cabin pressure in accordance with a ratio of cabinpressure to atmospheric pressure always at least as low as the blowercompression ratio.

23. The combination of claim 22, wherein the lastmentioned means isdirectly sensitive to cabin pressure and to atmospheric pressure, inratio equal to the selected blower compression ratio.

24. A system for the control of airflow through an aircraft cabin whichhas an inflow port and an outflow port, comprising: a blower of selectedcompression ratio connected to discharge compressed atmospheric airwithin the cabin through such inflow port; means to regulate outflowthrough such outflow port, to maintain continual outflow and toestablish cabin pressure at a value in excess of atmospheric pressure;means sensitive to the pressure difference thus created to automaticallycontrol said outflow-regulating means; and means operable under thejoint influence of cabin pressure and atmospheric pressurecompensatingly to control the outflow-regulating means to limit thepressure difference so that the ratio of cabin pressure to atmosphericpressure thus established never tends to exceed the blowers selectedcompression ratio.

25. Means to regulate the pressure within. an aircraft cabin,comprising: valve means to control outflow from the cabin, andconsequently the cabin pressure; differential-pressure sensitive meansoperatively connected to said valve means to adjust the same, andthereby to automatically prevent the cabin pressure exceedingatmospheric pressure by more than a selected diflerential pressurevalue; and means automatically operable in accordance with a selectedratio of cabin pressure to atmospheric pressure to adjust thedifferential-pressure sensitive means to limit the cabin pressurefurther, and thereby to prevent such selected ratio of cabin pressure toatmospheric pressure being exceeded.

26. Mechanism to control aircraft cabin pressures comprising, incombination with means to supply air under pressure within the cabin; anoutflow valve movable to regulate pressure within the cabin; pressureresponsive means operatively connected to move said valve to regulatethe degree of elevation of cabin pressure over exterior pressure; andmeans operable in accordance with a selected ratio of cabin pressure toatmospheric pressure, and operatively connected to said valve tooverride said pressure responsive means and to effect opening movementof said valve to prevent cabin pressure exceeding atmospheric pressureby more than said selected ratio of such pressures.

27. Mechanism to control ventilation through and pressure within anaircraft cabin whereinto air is continually supplied under pressure,comprising: an outflow valve open at all pressures for continuousoutflow; a pressure-sensitive means operatively connected to said valveto vary its opening and thereby to maintain cabin pressure elevatedabove atmospheric pressure; and further pressure-sensitive meansoperatively connected to modify the action of said firstpressure-sensitive means, and thereby to prevent the ratio of cabinpressure to atmospheric pressure exceeding a selected value.

28. Means to regulate aircraft cabin pressure, comprising: a blower tosupply air under pressure to the cabin; a valve arranged to controloutflow therefrom; actuating means operatively connected to the valve;control means operatively associated with said actuating means, andsubject to a difference of cabin pressure over atmospheric pressure,said actuating means and said control means being organized and arrangedto open the valve increasingly with decrease of atmospheric pressureafter the ratio of cabin pressure to atmospheric pressure reaches aselected value, thereby to prevent such ratio exceeding such value.

29. Mechanism to control flow of air through an aircraft cabin,comprising: means to supply within the cabin atmospheric air compresseda selected maximum compression ratio; a valve movable to control flow ofair through the cabin; and means operable in accordance with a selectedratio between cabin pressure over atmospheric pressure to move saidvalve for maintaining a pressure difference of cabin pressure overatmospheric pressure such that the ratio of cabin pressure toatmospheric pressure will never tend to exceed such selected maximumcompression ratio of said air supply means, for supply to the cabin of asubstantial quantity of air by said air supply means at all flightaltitudes.

30. Mechanism to regulate aircraft cabin pressure, comprising: means tosupply within the cabin atmospheric air compressed at a selected maximumcompression ratio; means regulating flow of air through the cabin; andcontrol means operable to govern said flow regulating means as theaircraft ascends through a lower altitude range to increase thedifferential of cabin pressure over atmospheric pressure, and as theairplane ascends to a higher altitude range operable to decrease thedifferential of cabin pressure over atmospheric pressure, so that theratio of cabin pressure to atmospheric pressure will not exceed theselected maximum compression ratio of said air supply means, therebyenabling said air supply means to deliver to the cabin a substantialquantity of air in such high altitude range.

31. Mechanism to regulate aircraft cabin pressure, comprising: anoutflow valve; an actuator operatively connected to move the valve, andthereby varying the rate of discharge of air from said cabin; and acontrol means operable automatically in accordance with the ratio ofcabin pressure to atmospheric pressure, operatively connected toregulate the resultant of the forces acting upon said actuator, andthereby the position of the valve and the cabin pressure, and to preventthe difference of cabin pressure over atmospheric pressure exceeding avalue corresponding to a selected ratio of cabin pressure to exteriorpressure.

32. In a control mechanism for a valve for controlling the relationshipof fluid pressures within a container to pressures outside the same, afirst pressure responsive means subjected to internal pressure andmovable in one direction in response to increase thereof, a secondpressure responsive means subjected oppositely to internal and externalpressures and movable in one direction in response to increase in thedifferential of internal over external pressure, a third pressureresponsive means subjected to external pressure and movable in onedirection in response to decrease thereof, valve means controlling theflow of fluid between the interior and exterior of the cabin, and meansto operate the valve means from said pressure responsive means, saidoperating means including connections to subject the valve means tooperation by the first or the second pressure responsive means,independently of each other so that the valve means responds to thefirst pressure responsive means so long as the resulting pressure doesnot exceed the maximum differential, and then responds to the secondpressure responsive means, and said operating means includingconnections to cause the third pressure responsive means to supplementthe moving force of the second pressure responsive means to effect amaximum ratio of internal to external pressure and to operate the valvemeans when internal pressure exceeds said maximum.

33. In a mechanism of the kind described for controlling therelationship of fluid pressures within a container to pressures outsidethe same, a housing having a first and a second chamber therein, thefirst chamber being subjected to internal pressure and the second toexternal pressure, a first pressure responsive means in the firstchamber resistingly movable in response to changes in internal pressure,a second pressure responsive means in the second chamber, means applyinginternal pressure to said second pressure responsive means so that itmoves in response to a difference in internal and external pressures, athird pressure responsive means in the second chamber movable inresponse to changes in external pressures, valve means adapted to beoperated by said pressure responsive means, and controlling fluid flowbetween the interior and exterior of the container, and connectionsbetween the first and second pressure responsive means and the valvemeans to eflect operation of the latter upon movements aforesaid of thesaid two pressure responsive means, and connections to cause the thirdpressure responsive means to coact with the second pressure responsivemeans when external pressure decreases below a predetermined value,whereby the valve means is operated to maintain a maximum ratio ofinternal to external pressure.

34. Mechanism to control ventilation through and pressure within asealed aircraft cabin, comprising: means for delivering air underpressure into said cabin; means to control the flow of air through thecabin; means operatively connected to said flow control means tomaintain cabin pressure at a value in excess of atmospheric pressure;and at least two pressure change sensitive instruments constantlysensing the changes in cabin absolute pressure and flight absolutepressure as said aircraft ascends and operatively interconnected tocoact, upon the attainment by said aircraft of an altitude at which theratio of cabin absolute pressure to flight absolute pressure is aselected ratio less than the compression ratio of said air deliveringmeans, to thereafter operate said flow controlling means to so regulatethe flow of air through the cabin as to maintain said selected ratiosubstantially constant as said aircraft ascends higher than saidaltitude whereby said air delivering means is maintained operative todeliver air into said cabin at all altitudes.

35. Mechanism to control ventilation through and pressure within asealed aircraft cabin, comprising: means for delivering air underpressure into said cabin; an outflow valve controlling the flow of airfrom the cabin; means for operating said valve to vary the rate ofdischarge of air from said cabin; means operatively connected to saidvalve operating means to maintain cabin pressure at a value in excess ofatmospheric pressure; and at least two pressure change sensitiveinstruments constantly sensing the changes in the ratio of cabinabsolute pressure to flight absolute pressure as said aircraft ascendsand operatively interconnected to coact, upon the attainment by saidaircraft of an altitude at which the ratio of cabin absolute pressure toflight absolute pressure is a selected ratio less than the compressionratio of said air delivering means, to thereafter operate said valveoperating means to so regulate the rate of discharge of air from thecabin as to maintain said selected ratio substantially constant as saidaircraft ascends higher than said altitude.

36. Mechanism to control pressure within an aircraft cabin whereinto airis continually supplied under pressure, comprising: an outflow valve; avalve control member operatively connected to said valve to effectmovement thereof; a pressure-sensitive element having one side thereofresponsive to cabin air pressure; means operatively connecting saidpressure-sensitive element to said valve control member to vary theopening of said valve, and thereby to maintain cabin air pressureelevated above atmospheric pressure; and a further pressure-sensitiveelement responsive to at least cabin air pressure and a connectiontherefor in said means interrupting, by movement 'of said furtherpressure-sensitive element, the action of 7 said firstpressure-sensitive element on said valve control member and substitutingthe control efiect of said further pressure-sensitive element to preventthe ratio of cabin air pressure to atmospheric pressure exceeding aselected value.

37. The mechanism defined in claim 36 in which the firstpressure-sensitive element is an evacuated bellows having its exteriorsubjected to cabin air pressure.

38. The mechanism defined in claim 36, and means to subject oppositesides of the first pressure-sensitive element respectively to cabin airpressure and to atmospheric pressure.

References Cited in the file of this patent or the origlnal patentUNITED STATES PATENTS 1,562,663 Strong Nov. 24, 1925 20 Gregg May 21,Price July 16, Wagner Dec. 9, Nixon et a1 Q. June 2, Del Mar Sept. 10,Del Mar Sept. 10, Del Mar Sept. 10, Cre'ver et a1 Feb. 10, Dube Feb. 8,Del Mar Apr. 17, Cooper et 'al Sept. 16,

FOREIGN PATENTS Great Britain May 27,

